This invention relates generally to electronic sound reproduction and more particularly to bell tone reproduction.
One known approach to digitally generating musical notes is a digital synthesizer which generates musical tones from a sequence of discrete data samples of the desired waveform. Enough samples of the waveform are stored in memory to define the structure of the waveform. The stored samples are then read out in a time sequence according to the pitch of the note selected on the keyboard or other similar device. To improve their sound quality, such synthesizers frequently use an interpolator to fill in the gaps between the sampled points. Additional components are used to perform the envelope shaping after the interpolator has determined the waveform. These systems require a lot of hardware and are not practical to fulfil the needs of a user who merely wants to repeatedly reproduce one type of sound, for example, a bell tone.
A bell tone is often desirable in alarm or warning systems. In general, the striking of a bell produces a sound, and thus a waveform, which changes over time. At the instant of the striking of a bell, a "strike frequency" is heard. As time progresses one or more "overtones," which are lower frequencies than the strike frequency, are heard over the strike frequency. Finally the bell will vibrate at its "resonant frequency," one that is lower than the overtone(s), until the next strike or until the bell loses its kinetic energy and stops vibrating. At any given time, all of these frequencies, and others which have amplitudes too small to be heard, are present in the bell's complex waveform, but the frequency with the largest amplitude is the one which is heard most prominently by the human ear.
It is an object of this invention to provide a simple electronic bell tone generator.